Flip chip assemblies interconnect semiconductor devices, such as integrated circuit chips and microelectromechanical systems (MEMS), to external circuitry with solder bumps that have been deposited onto the chip pads. These bumps are deposited on the chip pads on the top side of the wafer during final wafer processing. To mount the chip to external circuitry, such as a circuit board or another chip, it is inverted so that its top side faces down, and aligned so that its pads align with matching pads on the external circuit. The solder is then re-melted to produce an electrical connection, typically using a Thermosonic bonding or other reflow solder process. This leaves a small space between the chip's circuitry and the underlying mount. A dielectric adhesive may then be used to fill (underfill) this space to increase the strength of the mechanical connection and reduce stress on the solder joints due to thermal expansion differences between the chip and its surrounding elements: the underfill distributes forces generated during thermal expansion, which hinders stress concentration at the solder joints.
Flip chip assemblies are typically smaller than traditional carrier-based systems because the chip sits directly on the circuit board. Associated shorter wires reduce inductance, which allows higher-speed signals and better heat conduction. As such, flip chip assemblies can be well suited for a variety of electronic products.